Enamel composition

ABSTRACT

The present invention provides a composition for use in forming an enamel cover coat from which baked-on foods can be removed without the need for pyrolysis or highly alkaline cleaners. The enamel cover coat preferably exhibits no chipping or other surface defects subsequent to a 2.0 mm Plum Jam Test and an acid resistance of A or better according to ISO 2722. The composition according to the invention includes a glass component including at least a first glass frit comprising a low SiO 2  glass frit. Preferably, the glass component includes a blend of the first glass frit and at least a second glass frit. Preferably, the first glass frit includes by weight from about 30% to about 45% P 2 O 5 , from about 20% to about 40% Al 2 O 3 , from about 15% to about 35% Li 2 O+Na 2 O+K 2 O, up to about 15% B 2 O 3 , up to about 15% MgO+CaO+SrO+BaO+ZnO, up to about 10% TiO 2 +ZrO 2 , and up to about 10% SiO 2 .

FIELD OF INVENTION

The present invention provides an enamel composition. More particularly,the present invention provides a composition for use in forming an acidand chip resistant enamel cover coat from which baked-on foods can beremoved without the need for pyrolysis or highly alkaline cleaners.

BACKGROUND OF THE INVENTION

An oven can be one of the most difficult kitchen appliances to clean.Food that splatters onto the interior surfaces of the oven duringcooking usually becomes baked-on, making the removal thereofparticularly difficult. If the oven is not cleaned often, the amount ofbaked-on food can build up rapidly, thereby increasing the cleaningdifficulty.

There are several known methods for facilitating the removal of baked-onfood from the interior surfaces of ovens. The most widely used methodsinvolve pyrolysis or the application of highly alkaline chemical ovencleaners. Although these known methods are relatively effective forremoving baked-on food from the interior surfaces of ovens, they presentseveral disadvantages.

Many ovens feature a high-temperature “self-cleaning” cycle during whichbaked-on foods are pyrolyzed (i.e., decomposed) to carbon ash residuethat can be wiped from the interior surfaces of the oven once it cools.To be effective, such pyrolytic heating cycles must maintain thetemperature within the oven cavity above about 480° C. (900° F.) for aperiod of approximately 60 minutes.

One of the disadvantages of using pyrolysis to remove baked-on food fromthe interior surfaces of ovens is the tendency for the porcelain enamelsapplied to the interior surfaces of ovens to craze and in some casesflake off when they are repeatedly exposed to such elevatedtemperatures. Moreover, ovens having pyrolytic heating cycles are moreexpensive to manufacture than conventional ovens due to the need forextra insulation. Furthermore, such ovens are more expensive to operatethan conventional ovens because of the power consumed to generate andmaintain the high temperatures during the pyrolytic heating cycle. Suchovens can also present safety concerns because the exterior surfaces ofthe oven can become quite hot during the pyrolytic heating cycle.

Another method for facilitating the removal of baked-on food from theinterior surfaces of ovens involves the use of “catalytic” enamelcompositions such as the composition disclosed in Faust, U.S. Pat. No.4,084,975. Catalytic enamel compositions such as disclosed in Faust thathave been fired on the interior surfaces of ovens have a porous textureand contain a substantial quantity of metallic oxides that can catalyzethe oxidation of food material that is spilled or spattered on thesurface of the enamel. In operation, food material is absorbed into theporous enamel surface where the catalytic metallic oxides catalyzeoxidation of the food material at a substantially lower temperature thanis required for pyrolytic enamels.

One of the disadvantages of the use of catalytic enamels on the interiorsurfaces of ovens is that the pores in the enamel can rapidly becomesaturated and clogged with food material, which significantly diminishesthe ease with which the enamel can be cleaned. Furthermore, because thesurface of a catalytic enamel coating is porous, it is readily subjectto staining.

The other widely used method for removing baked-on food from theinterior surfaces of ovens involves the use of highly alkaline chemicaloven cleaners. Most oven cleaners of this type include significantquantities of caustics, such as sodium hydroxide and/or potassiumhydroxide. While such products are relatively effective in their abilityto remove baked-on food from the interior surfaces of ovens, they arehighly alkaline (pH typically greater than about 12) and thereforepresent safety hazards. Fumes from such products, which are best usedwhen the oven is warm, can irritate the eyes and throat and can alsocause chemical skin burns. Moreover, the resulting product of thechemical reaction between these cleaners and baked-on food is unpleasantto handle.

There exists a need for a composition that can be applied to theinterior surfaces of oven cavities and other articles from whichbaked-on foods can be removed without the need for pyrolysis or highlyalkaline cleaners.

SUMMARY OF INVENTION

The present invention provides a composition for use in forming anenamel cover coat from which baked-on foods can be removed without theneed for pyrolysis or highly alkaline cleaners. Preferably, the enamelcover coat produced using the composition according to the inventionexhibits no chipping or other surface defects subsequent to a 2.0 mmPlum Jam Test and has an acid resistance of A or better according to ISO2722.

The composition according to the invention comprises a glass componentcomprising at least a first glass frit. Preferably, the glass componentcomprises a blend of at least a first glass frit and a second glassfrit. Preferably, the first glass frit includes by weight from about 30%to about 45% P₂O₅, from about 20% to about 40% Al₂O₃, from about 15% toabout 35% Li₂O+Na₂O+K₂O, up to about 15% B₂O₃, up to about 15%MgO+CaO+SrO+BaO+ZnO, up to about 10% TiO₂+ZrO₂, and up to about 10%SiO₂. In the most preferred embodiment, the first glass frit comprisesby weight about 37.25% P₂O₅, about 31.67% Al₂O₃, about 12.42% K₂O, about11.16% Na₂O, about 3.78% B₂O₃, about 1.96% TiO₂, about 1.76% ZnO, andabout 0.00% SiO₂.

The present invention also provides a method of forming an enamel covercoat on a substrate from which baked-on foods can be removed without theneed for pyrolysis or highly alkaline cleaners. The method according tothe invention comprises providing a substrate; providing a compositioncomprising a glass component comprising at least a first glass fritcomprising a low SiO₂ glass frit; applying said composition to saidsubstrate; and firing said composition to form said enamel cover coat.The method according to the invention can be used to produce an enamelcover coat that has an acid resistance of A or better according to ISO2722 and that exhibits no chipping or other surface defects subsequentto a 2.0 mm Plum Jam Test.

The foregoing and other features of the invention are hereinafter morefully described and particularly pointed out in the claims, thefollowing description setting forth in detail certain illustrativeembodiments of the invention, these being indicative, however, of but afew of the various ways in which the principles of the present inventionmay be employed.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The enamel cover coat composition according to the present inventioncomprises a glass component comprising at least a first glass frit.Preferably, the glass component comprises a blend of at least two glassfrits. The first glass frit must be a low SiO₂ glass frit. As used inthe specification and in the appended claims, the term “low SiO₂ glassfrit” should be understood as meaning the total amount of SiO₂ smeltedinto the glass frit should be less than about 10% by weight, morepreferably less than about 4%, and most preferably 0.00%. The optionalsecond glass frit and any other glass frits further comprising the glasscomponent can any one or a combination of conventional refractory glassfrits such as, for example, the glass frits sold by Ferro Corporationunder the trade designations GL5, T1568, T394, 709, M488, 7001, and011-71-7004.

The low SiO₂ glass frit preferably comprises by weight from about 30% toabout 45% P₂O₅, from about 20% to about 40% Al₂O₃, from about 15% toabout 35% Li₂O+Na₂O+K₂O, up to about 15% B₂O₃, up to about 15%MgO+CaO+SrO+BaO+ZnO, up to about 10% TiO₂+ZrO₂, and up to about 10%SiO₂. More preferably, the low SiO₂ glass frit comprises by weight fromabout 35% to about 40% P₂O₅, from about 25% to about 35% Al₂O₃, fromabout 20% to about 30% Li₂O+Na₂O+K₂O, up to about 10% B₂O₃, up to about7% MgO+CaO+SrO+BaO+ZnO, up to about 7% TiO₂+ZrO₂, and up to about 4%SiO₂. The low SiO₂ glass frit can further comprise by weight up to about10%, and more preferably up to about 5%,MnO+CaO+NiO+CuO+Fe₂O₃+CrO₃+MoO₃+WO₃.

The currently most preferred and optimal ranges for the composition ofthe low SiO₂ glass frit in weight percent is shown below: Optimal OxideMost Preferred Range Range P₂O₅ 35.57-39.57 37.25 Al₂O₃ 30.00-34.0031.67 K₂O 10.00-14.00 12.42 Na₂O 10.00-13.00 11.16 B₂O₃ 2.00-5.00 3.78TiO₂ 0.00-3.00 1.96 ZnO 0.00-3.00 1.76 SiO₂ 0.00-1.00 0.00

The low SiO₂ glass frit may be prepared utilizing conventional glassmelting techniques. A conventional ceramic refractory, fused silica, orplatinum crucible may be used to prepare the low SiO₂ glass frit.Typically, selected oxides are smelted at temperatures of from about1200° C. to about 1450° C. for about 30 to 40 minutes. The molten glassformed in the crucible is then converted to glass frit usingwater-cooled steel rollers or water quenching. It will be appreciatedthat the step of producing the low SiO₂ glass frit is not per secritical and any of the various techniques well-known to those skilledin the art can be employed.

The low SiO₂ glass frit can comprise up to about 100% by weight of theglass component. More preferably, however, the low SiO₂ glass fritcomprises from about 20% to about 90% by weight of the glass component,with the balance of the glass component comprising one or moreadditional glass frits. In the presently most preferred embodiment ofthe invention, the low SiO₂ glass frit comprises from about 50% to about75% by weight of the glass component, with the balance of the glasscomponent comprising at least a second glass frit.

The glass frits comprising the glass component of the compositionaccording to the invention are preferably milled prior to application.Any of the conventional milling techniques can be employed. Millingfineness is not per se critical, but a fineness of about 2 cm³ beingretained from a 50 cm³ sample using a 200 mesh sieve is presentlyconsidered optimal.

It will be appreciated that the composition according to the inventioncan further comprise up to about 20% by weight of one or more milladditions. Suitable mill additions include, for example, clay,bentonite, magnesium carbonate, potassium nitrate, sodium aluminate,boric acid, and pigments. Inorganic materials, such as zirconia,alumina, alumina metaphosphate, spodumene, and feldspar, can also beadded to the composition in order to modify the texture and/or to adjustthe roughness of the fired enamel.

The surface texture of the fired enamel cover coat is generally lowgloss and slightly rough, yet still glassy and non-porous. The low SiO₂glass frit, if fired by itself, will generally produce a high glosssurface. The low gloss and slightly rough surface texture of the firedenamel cover coat according to the invention is believed to be aconsequence of the interaction between the low SiO₂ glass frit, which isrelatively soft, and the other glass frits, which tend to be relativelyharder. It has been determined that the addition of refractory milladded inorganic materials, such as ZrO₂ and/or Al₂O₃ for example, canalso lead to a slightly rougher surface texture, which can furtherimprove the ease with which the fired enamel cover coat can be cleaned.

The composition according to the invention is intended for use as acover coat. It can be applied like any of the known cover coat enamelsfor use on sheet steel. For example, it can applied directly ontopickled, nickel-coated steel. It can be applied over fired enamel groundcoated substrates. And, it can be applied over unfired ground coatsusing any of the well-known two-coat/one-fire processes (e.g., wet/wet,wet/dry, and dry/dry).

The composition according to the present invention can be applied by anyof the known wet application processes such as spraying, dipping, flowcoating, and electrodeposition. Preferably, the composition is driedprior to firing when it is applied using a wet application process.Drying is typically accomplished using heating lamps. The drying timeand temperature is not per se critical. The application rate of thecomposition by wet application processes will vary depending upon thedesired thickness of the resulting fired enamel cover coat. For example,a fired enamel cover coat having a thickness of about 140 μm can beobtained when the application rate of the wet enamel composition isabout 400 g/m².

The enamel composition can also be applied using conventional dryelectrostatic application processes. In such instances, anorganopolysiloxane is typically added to the composition to facilitateelectrostatic application. The application rate of the composition bydry electrostatic processes will vary widely according to the desiredthickness of the resultant enamel cover coat. Typical application ratesare from about 200 g/m² to about 600 g/m².

The composition according to the present invention is typically fired ata temperature of from about 770° C. to about 870° C. for about 2 toabout 8 minutes. More preferably, the composition is fired at atemperature of from about 800° C. to about 850° C. for about 3 to about6 minutes. The optimal firing conditions are 820° C. for about 3.5minutes. It will be appreciated that firing times and temperatures arenot per se critical, and a range of firing schedules could be used.

Upon firing, the composition according to the present invention forms anenamel cover coat from which baked-on foods can be removed without theneed for pyrolysis or highly alkaline cleaners. The enamel compositionaccording to the invention is particularly well-suited for applicationon the interior surfaces of oven cavities, dripping pans, cookware, andother articles that are exposed to the risk of baked-on food soiling.The fired enamel cover coat can be produced in a wide range of colors,including bright colors such as blue and green, simply by varying thepigments included as mill additions.

The fired cover coat enamel according to the invention is scratchresistant, stain resistant, and maintains its easy-to-clean propertiesover many heating cycles. In addition, baked-on food can be easilyremoved from the fired cover coat enamel without the need for hightemperature heating cycles or highly alkaline chemical cleaners. Mostbaked-on foods can be removed from the fired enamel cover coat usingwarm water. The fired cover coat enamel preferably exhibits an acidresistance of A or better according to ISO 2722, no chipping or othersurface defects subsequent to a 2.0 mm Plum Jam Test, and acceptablescores on the Modified FAN Test. The testing methods are describedbelow:

Plum Jam Test

In order to objectively compare the ease from which baked-on food can beremoved from fired enamel cover coats, Ferro Corporation developed the“Plum Jam Test.” According to the Plum Jam Test, two foods, being plumjam and olive oil, are each separately applied cold to the surface ofcold cover coat enameled coupons made of enameling grade steel (carboncontent about 0.05%) having the following dimension 13 cm×16 cm×1 mm.The olive oil used in the test is not critical. Any food grade olive oilcan be used. However, it has been determined that various factors suchas the pH, sugar content, and water content of the plum jam used in thetest can influence the results of the test. Accordingly, it is importantthat the plum jam used in the test be a plum jam sold as AachenerPfl{umlaut over (m)}li-Pflaumenmus, which is sold by Zentis of Germany,or a plum jam having the same performance characteristics as this plumjam.

The olive oil is applied dropwise to the coupons, and the plum jam isapplied at a thickness of 900 μm and 2 mm, respectively, using a brush.The coupons are then heated to a temperature of 280° C. for 30 minutesto bake the foods onto the coupon. After heating, the coupons areallowed to cool to room temperature. Once cooled, the coupons are soakedfor 5 minutes in 60° C. water containing 15 ml of ordinary householdliquid washing detergent per 5L of water. After soaking, the coupons areevaluated to determine the ease with which baked-on food could beremoved using a dry cloth and a two-sided common household cleaningsponge having both a soft side and an abrasive side according to thefollowing scoring system, where a score of 5 is considered best: StepCleaning Method Score 1 Surface of coupon completely cleaned by wipingwith a 5 dry cloth. 2 Surface of coupon completely cleaned by wipingwith 4 the soft side of a sponge and soaking solution. 3 Surface ofcoupon completely cleaned by wiping with 3 the abrasive side of a spongeand soaking solution. 4 Surface of coupon completely cleaned by wipingwith 2 the soft side of a sponge and liquid abrasive cleaner. 5 Surfaceof coupon can only be cleaned, if at all, by 1 wiping with the abrasiveside sponge and liquid abrasive cleaner.

Following the cleaning and scoring step, each coupon is evaluated forsurface defects such as chipping or marking.

Modified FAN Test

A second test used to objectively measure the ease with which baked-onfood can be removed from an enamel cover coat is the “Modified FANTest”. The letters “FAN” are an abbreviation of the French phrase facilea nettoyer, which translates to English as “easy-to-clean.” In theModified FAN Test, stainless steel retaining rings are adhered to thesurface of cover coat enameled coupons using a high thermal resistancesilicone sealing compound. 1 g. samples of the following foods are thenseparately applied within the stainless steel retaining rings cold tothe surface of cover coat enameled coupons: ketchup; lemon juice; saltedmilk; egg yolk; and gravy. The coupons are then placed in an airconvection oven at a temperature of about 250° C. for 30 minutes. Thecoupons are then removed from the oven and allowed to cool to roomtemperature. The stainless steel rings and polymerized silicone sealantare peeled off the coupons. The coupons are then soaked for 5 minutes in60° C. water containing 15 ml of ordinary household liquid washingdetergent per 5L of water.

After soaking, the coupons are evaluated to determine the ease withwhich baked-on food can be removed. Each coupon is wiped 3 times with atwo-sided common household cleaning sponge having both a soft side andan abrasive side (each wipe involves moving the sponge across the testarea and then back over the test area) and scored according to thefollowing system, where a score of 5 is considered best: Step CleaningMethod Pressure Score 1 Surface of coupon completely cleaned 1 kg 5 bywiping with abrasive side of sponge. 2 Surface of coupon completelycleaned 3 kg 4 by wiping with abrasive side of sponge. 3 Surface ofcoupon completely cleaned 6 kg 3 by wiping with abrasive side of sponge.4 Surface of coupon completely cleaned 6 kg 2 by wiping with abrasiveside of sponge and more detergent. 5 Same as step 4, but residueremains. 6 kg 1

The following examples are intended only to illustrate the invention andshould not be construed as imposing limitations upon the claims.

EXAMPLE 1

A low SiO₂ glass frit was prepared by smelting selected oxides in asmelting pot at about 1220-1270° C. for about 40 minutes and convertingthe molten glass to frit using water cooled rollers. The low SiO₂ glassfrit had the following composition: Component Wt. % P₂O₅ 37.25 Al₂O₃31.67 K₂O 12.42 B₂O₃ 3.78 Na₂O 11.16 TiO₂ 1.96 ZnO 1.76 SiO₂ 0

A wet enamel cover coat composition was formed using the low SiO₂ glassfrit by wet milling the following ingredients to a fineness of 2 cm³being retained from a 50 cm³ sample on a 200 mesh sieve: IngredientGrams Low SiO₂ glass frit 50 Ferro Frit 011-71-7004 50 Clay #2 5.5 K27,a synthetic bentonite sold 0.1 by Ferro Corporation Potassium carbonate0.2 Magnesium carbonate 0.1 Borax Decahydrate 0.2 Sodium nitrate 0.3FK3162, an inorganic spinel 2 type pigment sold by Ferro CorporationK64, a course (˜900 μm) 4 corundum sold by Ferro Corporation K101, analuminum 2 metaphosphate sold by Ferro Corporation

After milling, the wet enamel cover coat composition was applied to 13cm×16 cm×1 mm sheet steel coupons that had previously been coated with aconventional enamel ground coat. The wet enamel cover coat compositionwas applied using a spray gun at a rate of about 400 g/m². The wetenamel cover coat composition was dried using a heat lamp and then firedat about 820° C. for about 3.5 minutes producing an enamel cover coathaving a thickness of about 140 μm subsequent to firing.

The enameled coupons were tested for acid resistance in accordance withISO 2722 and for ease of baked-on food removal using the Modified FANTest and the Plum Jam Test as previously described. The results of thetesting are shown below: Test Score Acid Resistance ISO 2722 AA ModifiedFAN Test ketchup 5 lemon juice 5 salted milk 3 egg yolk 5 gravy 5 PlumJam Test olive oil 5 plum jam (900 μm) 5 plum jam (2.0 mm) 5

The enamel cover coat showed very good acid resistance, goodcleanability, and no chipping or other surface defects subsequent to the2.0 mm Plum Jam Test.

EXAMPLE 2

A dry enamel cover coat composition was formed using the low SiO₂ glassfrit prepared according to Example 1, using the following ingredients:Ingredient Grams Low SiO₂ glass frit 50 Ferro Frit 011-71-7004 50FK3162, an inorganic spinel 2 type pigment sold by Ferro CorporationK64, a course (˜900 μm) 4 corundum sold by Ferro Corporation K101, analuminum 2 metaphosphate sold by Ferro Corporation

These ingredients and about 0.2% by weight of an organopolysiloxane weredry milled together in a ball mill to a fineness of 8.0%±2.0% residuebeing retained on a 325 mesh sieve as determined using ASTM StandardC285-88. The resulting powder had a bulk resistivity of about 5×10¹⁵ohm/cm to about 80×10¹⁵ ohm/cm. After milling, the dry enamel cover coatcomposition was used for a two-coat/two-fire process and applied using astandard corona discharge gun at 50 kV to about 100 kV, on 13 cm×16 cm×1mm sheet steel coupons that had previously been coated with aconventional enamel ground coat. The application rate of the dry enamelcover coat composition was about 400 g/m².

The coupons were then fired at about 850° C. for about 6 minutes,producing an enamel cover coat having a thickness of about 150 μmsubsequent to firing. After cooling to room temperature, the couponswere tested for acid resistance and for ease of baked-on food removalusing the Plum Jam Test. Results are reported below: Test Score AcidResistance ISO 2722 AA Plum Jam Test olive oil 5 plum jam (2.0 mm) 5

The cover coat enamel showed very good acid resistance, goodcleanability, and no chipping or other surface defects subsequent to the2.0 mm Plum Jam Test.

EXAMPLE 3

A dry enamel cover coat composition was formed using the ingredientsaccording to Example 2. These ingredients and about 0.2% by weight of anorganopolysiloxane were dry milled together in a ball mill to a finenessof 8.0%±2.0% residue being retained on a 325 mesh sieve as determinedusing ASTM Standard C285-88. The resulting powder had a bulk resistivityof about 5×10¹⁵ ohm/cm to about 80×10¹⁵ ohm/cm.

After milling, the composition was used for a two-coat/one-firepowder/powder process and applied using a standard corona discharge gunat 50 kV to about 100 kV, on 13 cm×16 cm×1 mm sheet steel coupons. Thesecoupons had previously been applied with a commercial enamel ground coatsold by Ferro Corporation under the trade designation 076-78-9901 (theapplication rate of the ground coat was about 100-250 g/m² to obtain afired thickness of about 40 μm to about 90 μm). The application rate ofthe dry enamel cover coat composition was about 250 to about 400 g/m²(to obtain a fired thickness of about 90 μm to about 150 μm).

The coupons were then fired at about 850° C. for about 6 minutes. Aftercooling to room temperature, the coupons were tested for acid resistanceand for ease of baked-on food removal using the Plum Jam Test. Resultsare reported below: Test Score Acid Resistance ISO 2722 AA Plum Jam Testolive oil 5 plum jam (2.0 mm) 5

The enamel cover coat showed very good acid resistance, goodcleanability, and no chipping or other surface defects subsequent to the2.0 mm Plum Jam Test.

Baked-on food is easily removed from the fired enamel cover coataccording to the invention upon exposure to moist air for several hours.When the composition is applied to cookware and other submersiblearticles, baked-on food can be easily removed upon soaking the articlein hot (60° C. or higher) water for about 10 minutes. Oven cavities canbe cleaned by producing steam in the oven cavity or by applying hotwater to the interior surfaces of the oven using a sponge.

The present invention also provides a method of forming an enamel covercoat from which baked-on foods can be removed without the need forpyrolysis or highly alkaline cleaners. The method comprises providing asubstrate; providing a composition comprising a glass componentcomprising at least a first glass frit comprising a low SiO₂ glass frit;applying said composition to said substrate; and firing said compositionto form said enamel cover coat. Preferably, the glass componentcomprises a blend of said first glass frit and at least a second glassfrit. Moreover, said first glass frit preferably comprises by weightfrom about 30% to about 45% P₂O₅₁ from about 20% to about 40% Al₂O₃,from about 15% to about 35% Li₂O+Na₂O+K₂O, up to about 15% B₂O₃, up toabout 15% MgO+CaO+SrO+BaO+ZnO, up to about 10% TiO₂+ZrO₂, and up toabout 10% SiO₂. The enamel cover coat produced according to the methodof the present invention preferably exhibits excellent acid resistanceand no chipping or other surface defects subsequent to a 2.0 mm Plum JamTest.

It will be appreciated that the method according to the invention can beused to apply an enamel cover coat to pickled nickel-coated steel,decarburized and non-decarburized steel, and fired and unfired groundcoated substrates (by both 2 coat-2 fire and 2 coat-1 fire applicationprocesses).

The present invention is also directed to an article having at least onesurface coated with an enamel cover coat from which baked-on foods canbe removed without the need for pyrolysis or highly alkaline cleaners.The article can be, for example, an oven having the enamel cover coatapplied to the interior surfaces of the oven cavity, dripping pans, andcookware such as pots and pans. The enamel cover coated surface of thearticle according to the invention preferably exhibits excellent acidresistance and no chipping or other surface defects subsequent to a 2.0mm Plum Jam Test. The enamel cover coat is formed on the articleaccording to the invention by application of an enamel cover coatcomposition to a surface of the article and then firing the enamel covercoat composition. The enamel cover coat composition comprises a glasscomponent comprising at least a first glass frit comprising a low SiO₂glass frit, and more preferably a blend of said first glass frit and atleast a second glass frit. The first glass frit preferably comprises byweight from about 30% to about 45% P₂O₅, from about 20% to about 40%Al₂O₃, from about 15% to about 35% Li₂O+Na₂O+K₂O, up to about 15% B₂O₃;up to about 15% MgO+CaO+SrO+BaO+ZnO, up to about 10% TiO₂+ZrO₂, and upto about 10% SiO₂.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and illustrative examples shown anddescribed herein. Accordingly, various modifications may be made withoutdeparting from the spirit or scope of the general inventive concept asdefined by the appended claims and their equivalents.

1. A composition for use in forming an enamel cover coat from whichbaked-on foods can be removed without the need for pyrolysis or highlyalkaline cleaners, said composition comprising a glass componentcomprising at least a first glass frit, said first glass frit comprisinga low SiO₂ glass frit.
 2. The composition according to claim 1 whereinsaid glass component comprises a blend of at least said first glass fritand a second glass frit.
 3. The composition according to claim 2 whereinsaid enamel cover coat exhibits no chipping or other surface defectssubsequent to a 2.0 mm Plum Jam Test.
 4. The composition according toclaim 3 wherein said enamel cover coat has an acid resistance of A orbetter according to ISO
 2722. 5. The composition according to claim 3wherein said first glass frit comprises by weight from about 30% toabout 45% P₂O₅, from about 20% to about 40% Al₂O₃, from about 15% toabout 35% Li₂O+Na₂O+K₂O, up to about 15% B₂O₃, up to about 15%MgO+CaO+SrO+BaO+ZnO, up to about 10% TiO₂+ZrO₂, and up to about 10%SiO₂.
 6. The composition according to claim 5 wherein said first glassfrit further comprises by weight up to about 10%MnO+CoO+NiO+CuO+Fe₂O₃+CrO₃+MoO₃+WO₃.
 7. The composition according toclaim 5 wherein said first glass frit comprises by weight from about 35%to about 40% P₂O₅, from about 25% to about 35% Al₂O₃, from about 20% toabout 30% Li₂O+Na₂O+K₂O, up to about 10% B₂O₃, up to about 7%MgO+CaO+SrO+BaO+ZnO, up to about 7% TiO₂+ZrO₂, and up to about 4% SiO₂.8. The composition according to claim 7 wherein said first glass fritcomprises by weight from about 35.57% to about 39.57% P₂O₅, from about30.00% to about 34.00% Al₂O₃, from about 10.00% to about 14.00% K₂O,from about 10.00% to about 13.00% Na₂O, from about 2.00% to about 5.00%B₂O₃, up to about 3.00% ZnO, up to about 3.00% TiO₂, and up to about1.00% SiO₂.
 9. The composition according to claim 8 wherein said firstglass frit comprises by weight about 37.25% P₂O₅, about 31.67% Al₂O₃,about 12.42% K₂O, about 11.16% Na₂O, about 3.78% B₂O₃, about 1.96% TiO₂,about 1.76% ZnO, and about 0.00% SiO₂.
 10. The composition according toclaim 3 wherein said first glass frit comprises from about 20% to about90% by weight of said glass component.
 11. The composition according toclaim 3 wherein said first glass frit comprises from about 50% to about75% by weight of said glass component.
 12. The composition according toclaim 3 further comprising up to about 20% by weight of one or more milladditions.
 13. The composition according to claim 12 wherein at leastone of said mill additions is selected from the group consisting ofclay, bentonite, magnesium carbonate, potassium nitrate, sodiumaluminate, boric acid, and pigments.
 14. A method of forming an enamelcover coat from which baked-on foods can be removed without the need forpyrolysis or highly alkaline cleaners, said method comprising: providinga substrate; providing a composition comprising a glass component, saidglass component comprising at least a first glass frit, said first glassfrit comprising a low SiO₂ glass frit; applying said composition to saidsubstrate; and firing said composition to form said enamel cover coat.15. The method according to claim 14 wherein said glass componentcomprises a blend of at least said first glass frit and a second glassfrit.
 16. The method according to claim 15 wherein said enamel covercoat exhibits no chipping or other surface defects subsequent to a 2.0mm Plum Jam Test.
 17. The method according to claim 16 wherein saidfirst glass frit comprises by weight from about 30% to about 45% P₂O₅,from about 20% to about 40% Al₂03, from about 15% to about 35%Li₂O+Na₂O+K₂O, up to about 15% B₂O₃, up to about 15%MgO+CaO+SrO+BaO+ZnO, up to about 10% TiO₂+ZrO₂, and up to about 10%SiO₂.
 18. The method according to claim 16 wherein said substratecomprises pickled nickel-coated steel, fired enamel ground coated steel,or unfired enamel ground coated steel.
 19. An article having at leastone surface coated with an enamel cover coat from which baked-on foodscan be removed without the need for pyrolysis or highly alkalinecleaners, said enamel cover coat having been formed by applying acomposition to said surface of said article and then firing saidcomposition, said composition comprising a glass component comprising atleast a first glass frit, said first glass frit comprising by weightfrom about 30% to about 45% P₂O₅, from about 20% to about 40% Al₂O₃,from about 15% to about 35% Li₂O+Na₂O+K₂O, up to about 15% B₂O₃, up toabout 15% MgO+CaO+SrO+BaO+ZnO, up to about 10% TiO₂+ZrO₂, and up toabout 10% SiO₂.